Mercedes 560SEL hydraulic leveling system

Car rides rough, placed weight in trunk with engine running - no adjustment, I eliminated the struts and the accumulators, I have no leaks and the hydraulic fluid is clear. I read that the pumps typically are not the issue based on that I took a shot and assumed the position valve was leaking internally and not porting fluid. Everyone says the system is complicated? I think the pump is leaking within itself and not developing pressure, and therefore the rough ride and no movement. I replaced the valve and change the fluid (same issue). What is the accepted process of checking the pump pressure because no one touches on checking pressure which is the basis of how the system works? I read somewhere the pressure is about 3000 PSI seems high to me and scary. I am about ready to get some metric fitting and a gauge measure the pressure. I would assume there is a pressure regulator somewhere but have not read where there is one because that is where I should start.

I did take the car to the Mercedes dealer and the dealer said that cars rides a little rough but not bad and that if I wanted more performance then replace the accumulators and struts at $2,200.00. Unfortunately my confidence in this dealer is not high, a number of people suggested local shops which seems to be the wrong direction.

In summary the system should be easy to troubleshoot if you had good information available in the meantime I am guessing and that is expensive.

What help is there with regarding this system?

2 Answers

Very few want to work on these self-leveling systems. My understanding is
the rear end can NOT be converted to shocks/struts in the S Class - try
and find a dealer who can fix the system as is, but be prepared for a
ginormous bill.

First of all, I question their recommendation to replace the struts. In
Mercedes with SLS, the struts are merely hydraulic rams that do not
anything but raise or lower the car. If they aren't leaking externally,
they are good. They very rarely fail. The shock absorption is
performed by the accumulators which certainly do fail and there is no
way to tell by looking at them. Blown accumulators caused a rock
hard ride in the rear in my case.
I would recommend taking the car to a independent Mercedes or
European car shop. Do your research and find who is recommended in
your city. I own a 560SEL too and my independent Mercedes shop
was more than willing to replace the SLS system with 420SEL springs
and Bilstein HD shocks. That said, I opted to have my SLS system
repaired to keep the resale value and keep it original. Started by
replacing the 2 blown accumulators (use genuine Mercedes only, was
$196 each; the aftermarket ones don't last) and the rubber flex hoses
to them.
About 2 months after I had the accumulators and hoses to them
replaced, the leveling valve failed, causing the rear to sag and the
hydraulic pump started leaking externally. I replaced the leveling valve
with a new Mercedes OE one ($400) and purchased a rebuilt pump
with all new seals ($270). It is an expensive road to go down but I paid
less than $2200 total to have nearly the whole system replaced. The
SLS system should be reliable for about 10 years before I have to
start worrying about the accumulators again.
If you wish to tackle the job yourself, I highly recommend the SLS
troubleshooting and repair manual written by Kent Bergsma. It is
available on his website "wwww.mercedessource.com". He gives a
tremendous amount of information on how to diagnose any SLS issue
and how to replace various components. Unlike the factory manual, he
will tell you the quirks of the system and everything you need to look
out for. His manual describes the system in a W123 300TE wagon but
it's the same setup on the W126 560SEL.

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